Currently in magnetic recording technology, magnetoresistive (MR) sensors are used in MR heads in order to read data from magnetic media. For higher density recording applications, the MR sensors are typically giant magnetoresistive (“GMR”) sensors, such as spin valves.
FIG. 1 depicts a conventional MR sensor 10 that is typically used for reading data from a recording media (not shown). The conventional MR sensor 10 typically resides in a conventional read head that is incorporated into a conventional merged head that includes the conventional read head as well as a conventional writer. The conventional MR sensor 10 includes a conventional antiferromagnetic (AFM) layer 12, a conventional pinned layer 14, a conventional nonmagnetic spacer layer 16, a conventional CoFe sensor layer 18 and a conventional capping layer 20. The conventional capping layer 20 includes a conventional conductive layer 22 and a conventional capping layer.
The conventional pinned layer 14 and the conventional CoFe sensor layer 18 are ferromagnetic. The magnetization of the conventional pinned layer 14 is pinned in place by the conventional AFM layer 12. In certain conventional MR sensors (not shown) the conventional pinned layer 14 is a conventional synthetic pinned layer having two ferromagnetic layers that are antiferromagnetically coupled (AFC) and separated by a Ru layer. The magnetization of the conventional CoFe sensor layer 18 is free to rotate in response to an external magnetic field, such as one generated by the bits stored in a recording media. The conventional nonmagnetic spacer layer 16 is a conductive material, such as copper. In addition, CoFe/Cu interface is preferably surfactant treated by exposing the nonmagnetic spacer layer to oxygen. The conventional conductive layer 22 is typically composed of copper. The purpose of treating the nonmagnetic spacer layer 16 is to adjust the interlayer coupling between the conventional CoFe sensor layer 18 and the conventional pin layer 14 and to reduce the magnetostriction of the conventional CoFe sensor layer 18.
FIG. 2 depicts a conventional method 30 for fabricating the conventional MR sensor. The conventional AFM layer 12 is provided, via step 32. The conventional pinned layer 14 is then provided on the conventional AFM layer 12, via step 34. The conventional nonmagnetic spacer layer 16 is then fabricated, via step 36. The conventional CoFe sensor layer 18 is then provided, via step 38. The conventional capping layer 20, including the conventional conductive layer 22 and the conventional capping layer 24, are provided, via step 40.
Although the conventional MR sensor 10 formed using the conventional method 30 functions, one of ordinary skill with readily realize that as the thickness of the conventional CoFe sensor layer 18 is reduced, performance of the conventional MR sensor 10 degrades. For higher density recording applications, a sensor layer having a lower magnetization and, therefore, higher sensitivity to small magnetic fields is desired. As the thickness of the conventional CoFe sensor layer 18 decreases to less than or equal to approximately twenty Angstroms (particularly less than fifteen Angstroms), the magnetic properties of the conventional CoFe sensor layer 18 degrade. The coercivity of the conventional CoFe sensor layer 18 increases. In addition, the anisotropy field (Hk) increases. Because the conventional CoFe sensor layer 18 no longer has soft magnetic properties, the magnetization of the conventional CoFe sensor layer 18 does not readily change magnetic moment direction in response to an external field. In addition, the conventional CoFe sensor layer 18 may have very large magnetostriction. The dynamic range of the conventional MR sensor 10 is reduced and it becomes difficult to control the bias point of the conventional MR sensor 10. Furthermore, the MR effect decreases for thinner conventional CoFe sensor layers 18. Thus, the signal from the conventional MR sensor 10 is reduced. As a result, a conventional MR sensor 10 may be unusable at lower thicknesses of the conventional CoFe sensor layer 18.
Accordingly, what is needed is a system and method for improving the ability of MR sensors to function for higher density recording applications and, therefore, at smaller thicknesses of the sensor layer. The present invention addresses such a need.